A vanA vancomycin-resistant Enterococcus faecium ST80 outbreak resulting from a single importation event.

Area of Science:

• Microbiology
• Genomics
• Epidemiology

Background:

• A significant shift from vanB to vanA genotypes in vancomycin-resistant Enterococcus faecium (VREfm) occurred in Australia between 2011 and 2015.
• This shift is hypothesized to be driven by the emergence of multiple independent clones across different settings.

Purpose of the Study:

• To investigate the specific circumstances behind the vanB to vanA VREfm genotype shift within a single Australian hospital.
• To understand the introduction and spread dynamics of vanA VREfm.

Main Methods:

• Whole-genome sequencing of 69 vanA VREfm isolates collected between 2009 and 2018.
• Hybrid sequencing for detailed characterization of ST80 vanA VREfm isolates.
• Phylogenetic and plasmid sequence analysis to trace isolate origins and evolution.

Main Results:

• The 2011 expansion of ST80 vanA VREfm was linked to a single introduction event from an overseas patient in 2009.
• Phylogenetic analysis indicated limited spread beyond the local health district, suggesting a contained event.
• Plasmid analysis revealed multiple variants originating from the 2009 index isolate, demonstrating ongoing plasmid adaptation.

Conclusions:

• The findings confirm that a single VREfm introduction can lead to a prolonged clonal and plasmid outbreak.
• This study highlights the utility of hybrid sequencing in identifying epidemiological links to index cases.
• It underscores the complexity of countrywide VREfm genotype replacement events.